The present invention relates to magnetic coupling used in Ethernet over twisted pair networks.
An important step in the evolution of Ethernet local area networking was the transition from shielded coaxial cable as the transmission medium to unshielded twisted pair cable. Ethernet over twisted pair cable in the form of Cat5, Cat6, and variant cables is ubiquitous; such cables comprise four twisted pairs in a common jacket. Speeds have also evolved, from 10 Mbit/sec to 100 Mbit/sec (10/100 Ethernet) to 1 Gbit/sec (Gigabit Ethernet or GigE), with higher speeds being developed.
But with higher speeds comes an increased concern with radiated interference. In the United States, computing devices used in residential areas must meet stringent Federal Communications Commission (FCC) class B limits (Title 47 Part 15 Subclass B, Class B) for conducted and radiated emissions. The European Economic Community (EEC) has similar requirements under the IEC standard CISPR 22 (EN 55022). FCC limits cover conducted emissions from 0.45 MHz to 30 MHz, and radiated emissions from 30 MHz to at least 1 GHz.
Manufacturers of digital devices, particularly those putting high speed Ethernet connected devices into residential settings face an interesting problem in making such devices comply with International standards on emissions.